Inflammatory bowel disease (IBD), Crohn's disease or ulcerative colitis, affects an estimated 1.4 million Americans and is manifested by chronic inflammation of the gastrointestinal tract with significant morbidity and, at times, life-threatening complications. IBD is proposed to result from a dysregulated mucosal immune (innate and adaptive) response to the colonic flora in genetically susceptible individuals. Bacteroides fragilis is a common human commensal residing in the colon. A subset of B. fragilis, enterotoxigenic B. fragilis (ETBF), has been associated with inflammatory diarrheal disease, IBD, and colorectal cancer. Our ETBF murine model data shows that colonization with ETBF leads to a proinflammatory response exhibiting a predominant Th17 (interleukin 17-secreting) CD4+ T cell infiltrate promoted by signal transducer and activator of transcription-3 (Stat3) in C57BL/6 mice. The presence of activated Stat3 as well as colitis is evident within hours of orogastric inoculation with ETBF. However, there have been no investigations to date regarding the role of the innate immune system in ETBF colitis. IL-17 skewing has been recently demonstrated in a different infectious model involving downstream products of the Nucleotide-binding oligomerization domain containing (NOD) innate immune pathway. There is a strong association of NOD2 gene mutations and Crohn's disease. Hence, this data supports that innate immune factors and signal transducer and activator of transcription 3 (Stat3) plays a major role in the ETBF mouse model of colitis providing insight into the genesis of Inflammatory Bowel Disease. The objective of this research project is to address the role of the innate immune signaling pathways, in particular the NOD/Rip2 and toll like receptor (TLR)/MyD88, in the ETBF-induced colitis model. We will test the hypothesis that MyD88-/- and Rip2-/- mice will exhibit enhanced ETBF-induced colitis and Stat3 activation. To that end, the following Specific Aims are proposed: Specific Aim 1: To evaluate the role of NOD/Rip2 and TLR/MyD88 innate immune pathways in response of ETBF induced colitis using various genetically manipulated mice; Specific Aim 2: To define the role of Stat3 activation in the pathogenesis of ETBF-induced colitis in the NOD/Rip2- and TLR/MyD88- deficient mice; Specific Aim 3: To determine the role of TLR/MyD88 and NOD/Rip2 deficiency in hematopoietic versus non-hematopoietic derived cells on Stat3 activation and the pathogenesis of ETBF-induced colitis by creating and utilizing chimeric mice derived via bone marrow (BM) transplantation. The project will use the murine (C57BL/6) model of ETBF-induced colitis and various immunologic assays, knock-out mice, bone marrow transplantation, immunohistochemistry, flow cytometery, cytokine and RNA analysis. The significance of this research is that it will allow insight into the dysregulated immune response to colonic bacteria associated with IBD, a disorder with substantial morbidity, with hopes for new therapeutic insights to this prevalent disease.